What does a positive Lyme Immunoglobulin G (IgG) test result indicate?

From the Guidelines

A positive Lyme Immunoglobulin G (IgG) test result indicates that you have been infected with Borrelia burgdorferi, the bacterium that causes Lyme disease, at some point in the past, but it does not necessarily mean you have an active infection. IgG antibodies typically develop several weeks after infection and can remain in your bloodstream for years or even decades 1. This positive result should be interpreted alongside your clinical symptoms and possibly additional testing, as false positives can occur 1.

Key Points to Consider

• The sensitivity of the 2-tiered serologic analysis, which includes the IgG test, is low (30%–40%) during early infection, but it increases to 70%–100% for disseminated Lyme disease 1.
• The specificity of the test is high (>95%) during all stages of the disease 1.
• A positive IgG result is indicated by the presence of >5 of 10 specific bands on the Western immunoblot test 1.
• It is essential to avoid interpreting fewer bands as a positive overall result or evidence of infection because antibodies to several antigens are cross-reactive with non-Borrelial antigens 1.

Clinical Implications

• If you are experiencing symptoms consistent with Lyme disease, your healthcare provider may recommend treatment with antibiotics such as doxycycline (100mg twice daily for 10-21 days), amoxicillin, or cefuroxime, depending on your specific situation.
• Some patients may have persistent antibodies despite successful treatment, so the test cannot determine if treatment was effective or if reinfection has occurred.
• Always consult with your healthcare provider to properly interpret these results in the context of your overall health 1.

From the Research

Interpretation of Positive Lyme Immunoglobulin G (IgG) Test Result

• A positive IgG test result indicates the presence of IgG antibodies against Borrelia burgdorferi, the bacteria that causes Lyme disease 2.
• However, a positive IgG test result does not necessarily mean that the person has an active Lyme disease infection, as IgG antibodies can persist in the body for months or years after the infection has been cleared 3.
• The interpretation of a positive IgG test result should be accompanied by clinically suspected cases and a history of possible tick exposure 3.
• A positive IgG immunoblot is recommended to be interpreted as the recognition of two of five proteins (20,24,35,39, and 88 kDa) 2.

Diagnostic Criteria

• The diagnostic criteria for a positive IgG immunoblot include the recognition of specific proteins, such as 20,24,35,39, and 88 kDa 2.
• The sensitivity and specificity of IgG immunoblot for detecting patients who are seropositive during the study period were 54.6% and 93-96%, respectively 2.

Clinical Implications

• A positive IgG test result may not indicate an active infection, and therefore, should not be used as the sole basis for treatment decisions 3, 4.
• The presence of IgG antibodies may indicate a past infection, and the test result should be interpreted in the context of clinical symptoms and medical history 3, 4.